Tankless or flow-through heaters are known and are used to heat fluids (i.e. liquids and/or gases) while these media are being transferred to their point of use. Examples, where such flow-through heaters are typically used, are beverage brewing machines, such as household coffee makers, automotive windshield washer fluid heaters, hot water heaters for use in households and on board of aircraft, and in laboratory equipment.
Typical prior art flow-through heaters used in beverage brewing apparatus incorporate a heating element and a conduit-defining body which defines a conduit through which the media flows. Heat is transferred from the heating element, through the conduit-defining body, to the medium flowing through the conduit. In these prior art flow-through heaters, the local rate of heat transfer and the temperature distribution in the heaters are governed by the physical laws of heat conduction inside the conduit-defining body and heat convection where heat is transferred from the conduit-defining body to and through the fluid in the conduit. Typically, radiation heat-transfer mechanisms play a negligible role.
Prior art flow through heaters used in beverage brewing apparatus can generally be broken down into two design approaches. A first approach where the heating element is surrounded by the medium and the medium is contained by the conduit-defining body, and a second approach where the heating element is outside of the conduit-defining body and transfers its heat through the conduit-defining body to the medium flowing in the conduit itself.
In the first approach, where the heating element is immersed in the medium and is located inside the conduit-defining body, all heat generated is practically transferred to the medium, but a reliable seal is required where the heating element penetrates the conduit-defining body and into the medium. Providing a functional seal under thermal cycling conditions can pose reliability and cost challenges. Conversely, in the second approach, where the heating element is located outside of the conduit-defining body, not all heat can be transferred to the medium as there are losses to the environment away from the medium. However, the second approach preserves the integrity of the conduit, as all heating elements and their connections remain outside of the conduit, and a leak-proof design can be achieved with relative ease at relatively low cost.
Most known flow-through heaters used in beverage brewing apparatus seek to boil water. Boiling water causes undesirable scaling of the conduit-defining walls. Known prior art flow through heaters used for beverage brewing include those described, for example, in: U.S. Pat. Nos. 5,027,425; 5,111,740; and 8,107,803; and US patent publication No. 2010/046934.
Apart from the desire of heating fluid in a short period of time, there are a number of general desires in the field of flow-through heaters used in beverage brewing. These general desires include:                the desire to minimize the size of the heater or to otherwise make the heater more compact, permitting the heater to function under significant space constraints;        the desire to heat the medium to a desired (controllable) temperature, in a minimum possible time and with a minimum use of power; and        minimizing scaling on the conduit walls, since scaling lowers thermal conductivity, causing the temperature of the heating element to rise (due to the diminished heat transfer rate) and reduces the life expectancy of the heater.        
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.